/in/foo.c: In function 'main':
/in/foo.c:20:5: warning: implicit declaration of function 'bubbleSort' [-Wimplicit-function-declaration]
   20 |     bubbleSort(str);
      |     ^~~~~~~~~~
/usr/bin/ld: /tmp/ccCP0jl8.o: in function `main':
foo.c:(.text.startup+0x1f): undefined reference to `bubbleSort'
collect2: error: ld returned 1 exit status